Regenerative heat exchangers

ABSTRACT

A regenerative heat exchanger has a heat exchange mass in the form of a multilayer band of thin metal sheet, preferably many turns of a single strip or sheet of metal. Sealing of the band is effected by rollers between which it passes in traversing from one fluid path to the other. The band is driven by a bevel gear engaging the margin of the band, which is formed with gear teeth. The layers of the band are compressed together where they pass through the rollers, to minimize fluid carryover from one path to the other. Elsewhere, the layers are spread apart by spring tabs struck from the metal and bearing against adjacent layers so that a free path for flow of fluid is provided between the layers.

United States Patent [72] Inventor Oliver K. Kelley Bloomfield Hills,Mich. [21] Appl. No. 840,275 [22] Filed July 9, 1969 [45] Patented Mar.9, 1971 [73] Assignee General Motors Corporation Detroit, Mich.

[54] REGENERATIVE HEAT EXCHANGERS 21 Claims, 5 Drawing Figs.

[52] US. Cl 165/6, 165/10 [51] Int. Cl F28d 19/00 [50] Field ofSearch165/6, 10, 8, 9

[56] References Cited UNITED STATES PATENTS 2,866,624 12/1958l-lolmquist 165/6 2,915,297 12/1959 Lange 165/9 M l L PrimaryExaminer-Albert W. Davis, Jr. Attorneys-Paul Fitzpatrick and Jean L.Carpenter ABSTRACT: A regenerative heat exchanger has a heat exchangemass in the form of a multilayer band of thin metal sheet, preferablymany turns of a single strip or sheet of metal. Sealing of the band iseffected by rollers between which it passes in traversing from one fluidpath to the other. The band is driven by a bevel gear engaging themargin of the band, which is formed with gear teeth. The layers of theband are compressed together where they pass through the rollers, tominimize fluid carryover from one path to the other. Elsewhere, thelayers are spread apart by spring tabs struck from the metal and bearingagainst adjacent layers so that a free path for flow of fluid isprovided between the layers.

PATENTEDFAR 9 |97| sum 1 or 2 INVENTUR.

A M m REGENERATIVE HEAT EXCHANGERS My invention is directed toregenerative heat exchangers, particularly to an improved heat exchangematrix and driving and sealing means for such a matrix.

g A regenerative heat exchanger, as the term is used here, is a deviceproviding discrete passages for two streams of fluid, usually gases, andincluding a matrix which moves in a closed course so as to be exposedalternately to the fluids. The matrix absorbs heat from a hot fluid anddelivers heat to a colder fluid.

Such regenerators have received much consideration as elements of gasturbine engines because of the great contribution the regenerator maymake to the efficiency of the power plant, particularly under light loadconditions. In a gas turbine, the regenerator transfers heat frorntheexhaust gases leaving the turbine to compressed air delivered by thecompressor of the engine. Since the pressure ratio of such an engine isordinarily at least 2 /zto 1, there is ordinarily some or more poundsper square inch pressure difference between the two gases.

This present serious problems in the sealing of the matrix where itpasses through seals from one gas flow path to the other to prevent orminimize loss of compressed air. Another serious problem with respect toscaling is carryover losses. Since thematrix must be of a generallyporous or openwork nature to provide passages for flow of the fluids, aconsiderable amount of the compressed air is carried through in. thepores or voids of the matrix at the point where it moves from thecompressed air path to the exhaust path and is wasted in the turbineexhaust.

While it has long been known thatminimizing carryover losses and otherleakage losses in a regenerator is of great importance in increasing theefficiency of a gas turbine employing the regenerator, so far as I amaware there have been no schemes for minimizing carryover loss in thematrix which have proved sufficiently practical for commercial adoption.Examples of prior art proposals along this line embodied in U.S. Pat.Nos. 2,915,297 to Lange for Regenerative Heat Exchanger with MovableMatrix, Dec. 1, 1959; No. 2,938,713 to Collman for Regenerative HeatExchanger, May 31, 1960; and No. 3,155,151 to Pouit for Heat Exchangers,Nov. 3, 1964.

My invention is directed to providing a regenerative heat exchangerhaving improved structure and improved operating characteristics overpreviously known devices.

The principal object of my invention is to provide regenerators havingimproved characteristics so far as heat transfer efficiency,minimization of leakage and carryover of fluid, and durability andeconomy of manufacture are concerned. A further object is to provideimproved driving means for a multilayer regenerator band whicheffectively maintains synchronism and provides for separation of thelayers of the band. A further object is to provide a multilayer heatexchange matrix having inherently self-separating layers which may bepressed together to expel fluid at the point where the matrix passesthrough a seal from one fluid path to another. An ultimate object of myinvention is to improve the efficiency, economy, and commercialfeasibility of regenerative gas turbine engines.

My invention is primarily concerned with a heat exchanger matrixcomposed preferably of a single continuous thin sheet metal band formedinto a number of nesting or coiled layers, with each layer from theinnermost outward being progressively longer to allow for uniformclearance between all the layers. The matrix may, however, be made up oftwo or more thin sheet metal bands coiled in alternating relationship.

My invention also is concerned with driving means to drive each layer ofthe matrix at a linear speed proportional to its length so as to achieveequal heating and cooling of all layers of the matrix and also toachieve substantially equal angular movement of all layers around acentral point in an arc of movement so as to minimize relative slidingmovement between the layers.

My invention also is concerned with sealing means which minimize theclearance between the matrix and the bulkhead which separates thehigh-pressure and low-pressure fluids. This is preferably achieved withseals in rolling contact with the matrix at the bulkhead.

It is an important concern of my invention to minimize both directleakage through the seals from high pressure to low pressure andcarryover losses which result from the transportation of gas entrappedin the voids of the matrix from one fluid path to the other, regardlessof the pressure differential. The carryover loss is the more difficultproblem of the two, so far as sealing is concerned. According to myinvention, such carryover loss is substantially eliminated, thus makingpossible many advantages including a higher rate of movement of thematrix without accompanying penalties or higher compression ratios ofthe engine without higher penalties from carryover losses. l I

A very important concern of my invention is layer separating means builtinto the layers of the matrix which achieve and assure maintenance ofsubstantially uniform desired spacing between adjacent layers of thematrix. It will be understood that, with a regenerator embodying thinsheets of metal, the effectiveness of the heat exchanger decreases asthe spacing between the sheets or layers increases; however, with tooclose spacing, proper flow is impeded. With sheets approximately 0.002inch thick, the optimum spacing is something like 0.015 inches. Thus, itis desirable that the layers of the matrix maintain a small constantspacing from near the main seals all the way around as closely aspossible to the point at which they reenter the main seals.

Also, with the thin sheets in a current of rapidly flowing gas, it isimportant to eliminate flutter of the sheets. Both these ends areachieved, according to my invention, by the provision of integral springtabs extending outward from each layer or from alternate layers so as tocreate an inherent tendency of the layers to separate to a desiredextent and to damp incipient flutter while permitting the layers to beclosed together while passing through the seal to eliminate thecarryover.

According to a feature of the invention, the spring tabs which actuatethe spacing of the sheets and control any tendency to flutter also serveto create a'desired degree of turbulence in the flow thus speeding thetransfer of heat between the matrix and the gas. As a result, a smallerarea of heat transfer sheets may be employed in the matrix.

The nature of my invention and its advantages will be apparent to thoseskilled in the art from the succeeding detailed description of preferredembodiments of the invention and the accompanying drawings thereof.

FIG. 1 is a somewhat schematic sectional view of a regenerator.

FIG. 2 is a sectional view of the heat exchanger, with parts cut away,taken on broken planes indicated generally by the line 2-2 in FIG. 1.

FIG. 3 is a fragmentary enlarged view of a portion of the matrix asviewed in FIG. 1.

FIG. 4 is a view similar to FIG. 3' illustrating a different form ofmatrix.

FIG. 5 is a fragmentary plan view of a matrix sheet or layer.

Referring first to FIG. 1, the regenerator 10 includes an outer case 11and an inner case 12 of roughly figure eight shape which defines betweenthem an arcuate cool air path 14 and an arcuate hot gas path 15 or, ingeneral, paths for two fluids at 14 andlS, the two fluids flowing in adirection perpendicular to the plane of the figure and preferably inopposite directions. The outer case 11 and inner case 12 define betweenthem a track or path for a heat exchange matrix 16 which is an endlessflexible structure made up of thin sheet metal in the form of amultilayer band which slowly traverses the track between the outer andinner walls. The track could be circular or any desired closed curve butthe preferred form is generally as illustrated. In a typical applicationof the regenerator, the cool air path conducts air from the compressorof a gas turbine engine to the combustion apparatus of the engine andthe hot gas path conducts exhaust gas from the turbine to the engineexhaust. The matrix continually circulates in the closed path definedbetween the inner and outer walls, any portion of the matrix thuspassing successively through the hot gas and the cool air and serving totransfer heat from the hot gas to the cool air. The two gas paths may beof unequal size, as illustrated.

The air and gas paths are separated from each other and the matrix isdriven by the matrix sealing and driving assembly 18 disposed betweenthe two fluid paths. Referring also to FIG. 2, the sealing and drivingassembly 18 is mounted in the outer case 11 which at this point includesa rear wall 19 disposed between the air and gas paths and which alsoincludes a cover plate 20 likewise disposed between the air and gaspaths, the ends of which are indicated by the dotted lines at 22 inFIG. 1. The sealing and driving assembly includes a main or driving roll23 and preferably four sealing rolls 24. The matrix is fed between thedriving roll and two of the sealing rolls as it passes from each of thetwo fluid paths to the other. Before proceeding'further to describe thesealing and driving assembly, it may be best to consider more fully thenature of the matrix itself.

The structure of the matrix will be more clearly apparent from FIGS. 3,4, and 5. It is made up of many layers of thin sheet metal preferablymade by coiling a single continuous band. For example, in a particularcase, the matrix might comprise 250 layers of metal, each of 0.002-inchstock. While conceivably each layer could be a closed band, it is highlyadvantageous to have the matrix made of a single multiturn strip, or afew such strips, so as to avoid numerous joints, one for each layer ofthe matrix, in the endless band.

Referring first to FIG. 3 which shows several layers of the matrixidentified as the outermost layer 26 and intermediate layers 27, all ofthe layers except the outermost layer are formed with spring tabs 28struck out from the sheet extending from the sheet in the direction awayfrom the direction of motion of the matrix indicated by the arrow 30.

The tabs 28 may take any suitable form such as that indicated in FIG. 5.The arrangement of the tabs is largely a matter of choice and sounddesign. They may be in echelon as illustrated or in a rectangularpattern.

When there is no force pressing the layers of the matrix together, thesetabs extend slightly from each surface of the sheet 27 and serve toseparate the layers of the matrix to provide for flow of gas between thelayers. When the matrix is passed between rollers 23 and 24, the tabsare flattened into the plane of the tabbed sheets and the matrix iscompacted so as to expel substantially all of the air or gas whichotherwise might be carried through the seal in the voids of the matrix.

An alternative form of the matrix is shown in FIG. 4 in which the matrixis made up by wrapping two alternating sheets, one being a plain sheet31 and the other being a tabbed sheet 32. In this case, the tabbed sheethas tabs 33 extending from both surfaces of the sheet so as to bearagainst both of the adjacent plain sheets 31. In this case the directionof motion is to the right as illustrated, the same as in FIG. 3. Theleading edges of the two outer layers are attached by welding asindicated at 35 so that they will track the other layers through therolls. In all cases the leading end of the sheet, whether at the insideor the outside of the matrix, should be somehow secured so that itcannot double back and is pulled along by the sheet next to it.

At this point it may also be mentioned that the tabs 28 or 33 arefurther useful in creating turbulence in the fiow of gas through thematrix which is obstructed by the tabs in the path of flow. By breakingup laminar boundary layer flow, heat transfer to or from the matrix isimproved. The tabs may be inclined to the direction of flow or skewed soas not to be exactly edge-on to the gas flow so as to increase theturbulence created by the tabs.

A suitable material for the matrix is a high temperature stainless steelwhich retains its elastic properties at the high temperature levelencountered in a regenerator.

Returning now to consideration of the matrix sealing and drivingarrangement with reference primarily to FIG. 2, roll 23 is on the innerside of the matrix band and rolls 24 are on the outer side. The rollscause the matrix to be convex outwardly at the point where it passesthrough the seal in an arcuate path. This arcuate path is needed tocause the matrix to mesh properly with two driving bevel pinions 41. Oneedge, as shown, of the matrix 16 bears gear teeth 42 which areprogressively larger, or at least of progressively greater spacing, fromthe inner side of the matrix at roll 23 to the outer side of the matrixat rolls 24. This progressive increase in spacing of the teeth causesthem to mate properly with the tapered teeth 43 of the bevel pinions 41when the matrix is curved around roll 23 to cause the teeth to define asegment of a bevel gear at the driving point.

Because of the separation of the layers of the matrix as it movesthrough the heat exchange path, it is necessary for the outer layers ofthe matrix to move farther than the inner layers, and it is extremelydesirable that all layers make the circuit in the same time; therefore,the outer layers should move faster than the inner. By proportioning theincrease in pitch of the matrix teeth and of the mating bevel gear teethfrom the inner side to the outer side of the matrix to the difference inlength of path of each layer, the entire matrix moves together insynchronism without significant slip between the layers or any tendencyto wind up or unwind the matrix c9i coil. Thus, the rolls 24 are soplaced as to cause the matrix to follow the arc of the teeth of thebevel gears which, of course, enter into and leave the teeth in themargin of the matrix as the matrix passes the gear. All of rolls 23 and24 are rotatably mounted by stub shafts journaled in the case wall 19and cover 20 except that one end of roll 23 is supported by an inputshaft 61 journaled in the cover and splined at 62 to the main roll.Shaft 61, which provides the drive for the matrix, also is journaled ina nonrotating block or flow-blocking member 63 one face of which abutsan end of driving roll 23. Two bevel pinions 41 disposed normal to theaxis of shaft 61 and roll 23 are mounted on stub shafts, the inner endsof which are journaled in the block 63 and the outer ends of which arejournaled in the cover 20. A driving bevel gear 66 on the end of roll 23engages teeth of the bevel pinions 41 which extend outwardly beyond theroll and are in driving engagement with teeth 42 of the matrix. Thrustwashers 67 at the outer ends of the bevel pinions and 68 at the innerends of the pinions engage the cover 20 and the block 63, respectively,and serve to block fluid flow past the seal. The outer washers 67 engagethe ends of rolls 24.

An idler bevel gear 70, freely rotatable on shaft 61, meshes with thebevel pinions 41 and thus serves to block off leakage or carrythrough bythe teeth of the bevel gears. As will be seen, the structure includingblock 63 closes any bypass around that edge of the matrix. At the otheredge of the matrix a conical-faced disc 71 defined by a flange on theroll 23 engages the other edge of the matrix to resist the bevel gearside thrust and to seal against leakage at that edge. Slight clearancesmay be provided between the parts to allow for differentials ofexpansion when the apparatus heats and cools but, as will be seen, thereis no significant leakage clearance and the apparatus may be designed sothat the leakage clearances are minimized at operating temperatures ofthe structure.

The matrix 16 as it loops through the cool air and hot gas sections ofthe regenerator is guided in arcuate paths and allowed to open up due tothe spring action of the tabs on sheets 35 to a desired degree toprovide passages for flow of gas between the sheets. The degree ofopening up of the matrix is controlled preferably by engagement of theoutermost and innermost sheets with the walls 11 and 12 of the track,respectively. Since these sheets may be in frictional engagement withthe walls, they preferably are plain or untabbed.

While there may be variations in the dimensions and constants of thestructure to suit desired conditions, it may be informative to set outsome dimensional values with respect to a preferred embodiment. In thisexample, the tabs are 0.37 inches long and extend from the surface inthe unstressed condition a distance of 0.03 inches. Insuch case, theymay run with the sheets at the nominal spacing of 0.015 inch and, insuch case, the tabs can exert a sufficient separating force per inch ofstrip length to bias the matrix against the inner and outer guidingstructures and to stabilize the strips with substantially evenspacingbetween the guiding walls. With such a structure, in a 6 inch-widestrip, a separating force of approximately 0.14 pounds per inch of striplength could be provided. As the strips emerge from the rolls, the tabswould exert an initial force of twice the value to open the matrix earlyafter its emergence from the roll. I

It should be apparent to those skilled in the art from the foregoingdescription of preferred embodiments of my invention that it is indeedadapted to provide better regenerators and thus improve performance ofgas turbine engines incorporating regenerators. The structure results inbetter sealing between the gases at two different pressures and insubstantially complete elimination of carryover through the main sealsin the matrix. It also eliminates many of the structural problems ofrigid matrix discs and drums.

Furthermore, the structure is relatively inexpensive, since the matrixitself is merely lanc'ed out. sheets, plus flat sheets if desired. Theformation of the gear teeth in the matrix may e be accomplished by anysuitable machining or punching technique, gradually increasing thespacing-of the teeth from the inner side to theouter side of the matrixin accordance with the changes in length of the loops of the matrix andthe accompanying change in spacing of the driving bevel gear teeth.

The detailed description of preferred embodiments of the vancing meansincludes rolls engaging opposite faces of the invention for the purposeof explainingthe principles thereof is not to be considered as limitingor restricting the invention, since many modifications may be made bythe exercise of skill in the are without departing from the scope of theinvention.

lclaim:

'1. A heat exchanger comprising, in combination, a housing defining aclosed track for aheat transfer matrix and defining distinct paths fortwo fluids across the track, a continuous heat exchange matrix extendingaround the track through the said paths, and means disposed betweenthe'paths for progressively advancing the matrix around the track,.-thematrix being formed by a large number of layers, each layer being athin sheet of elastic material, at least someof the layers, bearingspring tabs normally biasing the layers apart for flow of fluid betweenthe layers, and the advancing means including means for pressing thelayers together at the advancing means.

2. A heat exchanger as defined in claim 1 in which the advancing meansincludes a tapered driving gear and the band has gear teeth engaging thegear, the number of such gear teeth being the same on each layer of thematrix.

1 3. A heat exchanger as defined in claim 2 in which the advancing meansincludes means for guiding the matrix in an arcuate path so that thesaid gear teeth define a segment of a bevel gear at the area ofengagement with the driving gear.

4. A heat exchanger asdefined in claim 1 in which a single sheet ofelastic material makes a plural number of turns to define a pluralnumber of layers of the matrix.

5. A heat exchanger as defined in claim 1 in which the matrix hasalternating plain and tab-bearing layers, each matrix for pressing thelayers together.

9. A regenerative heat exchanger comprising, in combination, a housing,means defining a first path through the housing for a first fluid, meansdefining a second path through the housing for a second fluid, amultilayer continuous heat exchange band having a portion disposed ineach path, and means disposed in the housing between the paths fortraversing the band through the paths and for providing a seal betweenthe paths comprising a roll engaging each face of the band, sealingmeans engaging one edge of the band, and a banddriving bevel gearengaging the other edge of the band,

. the said other edge having teeth to engage the bevel gear.

10. A heat exchanger as defined in claim 9 in which the heat exchangeband comprises two alternating sheets, one including resilient means toseparate the sheets, and in which each sheet continues through amultiplicity of turns to define a multiplicity of layers of the band.

11. A heat exchanger as defined in claim 9 in which the heat exchangeband comprises a multiplicity of abutting turns of single sheetincluding resilient means to separate the turns.

12. A heat exchanger as defined in claim 9 in which one said rollincludes means coupling it to the said bevel gear to drive the bevelgear.

13. A regenerative heat exchanger matrix comprising a continuousflexible multilayer band formed by a plurality of turns of thin flexiblemetal sheet with successive layers of the band in face-to-face abuttingunbonded relation and with spring means within the band yieldablybiasing the layers apart.

14. A matrix as defined in claim 1'3 defined by abutting turns of asingle sheet bearing leaf springs extending from the sheet to bearagainst an adjacent .turnof the sheet. 15. A matrix as defined in claim13 defined by alternate turns of a plain sheet and of a sheet bearingleaf springs engaging the plain sheet.

16. A matrix as defined in claim 13 in which the band has gear teeth inat least one edge.

17. A matrix as defined in claim 16 in which the number of gear teeth isthe same in all layers and the spacing of the gear teeth variesprogressively from inside to outside of the edge of the band.

18. A regenerative heat exchanger matrix comprising a continuousmultilayer band formed by a plurality of layers of a single thin metalsheet with successive layers of the sheet in face-to-face relation, thesheet bearing spring tabs unitary with the sheet projecting from thesheet to bias abutting layers apart for fluid flow between the layers,the tabs being elastically deformable substantially into the plane ofthe layer by exertion of compressive force on the band.

19. A matrix as defined in claim 18 in which the band is formed withgear teeth at one edge.

20. A matrix as defined in claim 19 in which the pitch of the gear teethvaries progressively from face to face of the band.

21. A regenerative heat exchanger comprising, in combination, acontinuous multilayer heat exchange band formed by a plurality of layersof thin sheet, and sealing and driving means for the band comprising adriving roll; two idler rolls disposed adjacent to and spacedcircumferentially aroundthe driving roll, a disc at one end of thedriving roll engaging the idler rolls, a driving bevel gear on the otherend of the driving roll, two bevel pinions rotatable on axesintersecting the axis of the driving roll and driven by the drivingbevel gear, an idler bevel gear coaxial with the driving roll meshingwith the bevel pinions, a flow blocking member closing the spaceoutlined by the bevel gears and bevel pinions, the band being disposedbetween the driving roll and each of the idler rolls, the disc engagingone edge of the band and the bevel pinions engaging the other edge ofthe band.

1. A heat exchanger comprising, in combination, a housing defining aclosed track for a heat transfer matrix and defining distinct paths fortwo fluids across the track, a continuous heat exchange matrix extendingaround the track through the said paths, and means disposed between thepaths for progressively advancing the matrix around the track, thematrix being formed by a large number of layers, each layer being a thinsheet of elastic material, at least some of the layers bearing springtabs normally biasing the layers apart for flow of fluid between thelayers, and the advancing means including means for pressing the layerstogether at the advancing means.
 2. A heat exchanger as defined in claim1 in which the advancing means includes a tapered driving gear and theband has gear teeth engaging the gear, the number of such gear teethbeing the same on each layer of the matrix.
 3. A heat exchanger asdefined in claim 2 in which the advancing means includes means forguiding the matrix in an arcuate path so that the said gear teeth definea segment of a bevel gear at the area of engagement with the drivinggear.
 4. A heat exchanger as defined in claim 1 in which a single sheetof elastic material makes a plural number of turns to define a pluralnumber of layers of the matrix.
 5. A heat exchanger as defined in claim1 in which the matrix has alternating plain and tab-bearing layers, eachdefined by a plural number of turns of a single sheet.
 6. A heatexchanger as defined in claim 1 in which the matrix is made up byabutting coils of a single tab-bearing layer.
 7. A heat exchanger asdefined in claim 1 in which the track includes means limiting the extentof such biasing.
 8. A heat exchanger as defined in claim 1 in which theadvancing means includes rolls engaging opposite faces of the matrix forpressing the layers together.
 9. A regenerative heat exchangercomprising, in combination, a housing, means defining a first paththrough the housing for a first fluid, means defining a second paththrough the housing for a second fluid, a multilayer continuous heatexchange band having a portion disposed in each path, and means disposedin the housing between the paths for traversing the band through thepaths and for providing a seal between the paths comprising a rollengaging each face of the band, sealing means engaging one edge of theband, and a band driving bevel gear engaging the other edge of the band,the said other edge having teeth to engage the bevel gear.
 10. A heatexchanger as defined in claim 9 in which the heat exchange bandcomprises two alternating sheets, one including resilient means toseparate the sheets, and in which each sheet continues through amultiplicity of turns to define a multiplicity of layers of the band.11. A heat exchanger as defined in claim 9 in which the heat exchangeband comprises a multiplicity of abutting turns of single sheetincluding resilient means to separate the turns.
 12. A heat exchanger asdefined in claim 9 in which one said roll includes means coupling it tothe said bevel gear to drive the bevel gear.
 13. A regenerative heatexchanger matrix comprising a continuous flexible multilayer band formedby a plurality of turns of thin flexible metal sheet with successivelayers of the band in face-to-face abutting unbonded relation and withspring means within the band yieldably biasing the layers apart.
 14. Amatrix as defined in claim 13 defined by abutting turns of a singlesheet bearing leaf springs extending from the sheet to bear against anadjacent turn of the sheet.
 15. A matrix aS defined in claim 13 definedby alternate turns of a plain sheet and of a sheet bearing leaf springsengaging the plain sheet.
 16. A matrix as defined in claim 13 in whichthe band has gear teeth in at least one edge.
 17. A matrix as defined inclaim 16 in which the number of gear teeth is the same in all layers andthe spacing of the gear teeth varies progressively from inside tooutside of the edge of the band.
 18. A regenerative heat exchangermatrix comprising a continuous multilayer band formed by a plurality oflayers of a single thin metal sheet with successive layers of the sheetin face-to-face relation, the sheet bearing spring tabs unitary with thesheet projecting from the sheet to bias abutting layers apart for fluidflow between the layers, the tabs being elastically deformablesubstantially into the plane of the layer by exertion of compressiveforce on the band.
 19. A matrix as defined in claim 18 in which the bandis formed with gear teeth at one edge.
 20. A matrix as defined in claim19 in which the pitch of the gear teeth varies progressively from faceto face of the band.
 21. A regenerative heat exchanger comprising, incombination, a continuous multilayer heat exchange band formed by aplurality of layers of thin sheet, and sealing and driving means for theband comprising a driving roll, two idler rolls disposed adjacent to andspaced circumferentially around the driving roll, a disc at one end ofthe driving roll engaging the idler rolls, a driving bevel gear on theother end of the driving roll, two bevel pinions rotatable on axesintersecting the axis of the driving roll and driven by the drivingbevel gear, an idler bevel gear coaxial with the driving roll meshingwith the bevel pinions, a flow blocking member closing the spaceoutlined by the bevel gears and bevel pinions, the band being disposedbetween the driving roll and each of the idler rolls, the disc engagingone edge of the band and the bevel pinions engaging the other edge ofthe band.